The present application is directed to certain concrete compositions which have unexpectedly been found to completely substantially inhibit corrosion of metal pieces contained therein over a sustained period of time. The present invention is directed to a corrosion inhibiting concrete composition comprising a high strength concrete formed from a hydraulic cement and which contains at least about 2 percent calcium nitrite therein.
Concretes formed from hydraulic cements, of which portland cement is the most common example, are used as structural components in various applications, such as in the formation of roads, bridge deckings, building structures, multistory automobile storage structures and the like. In order to enhance the properties of the concrete to permit its utilization in these manners, the material normally is used in combination with iron or steel reinforcing structures therein. These reinforcing metal structures, usually in the form of metal rods or bars, are subjected to attack by the various corrosive elements contained in the concrete, as well as by the application of external corrosive elements to the structure, such as chloride salts and the like, which are commonly used in the removal of ice and snow from roads, bridges, pedestrian walkways and the like. Further, various structures located at coastal installations and the like are subject to corrosive salt attack from the environment. The repair and replacement of such structures which have deteriorated due to the effects of such corrosive forces is extensive and in certain instances requires complete replacement of the structure, as it is unsuitable for its intended use.
In attempts to counteract the corrosive effects normally encountered by concrete structures, as discussed above, various corrosion inhibiting agents have been proposed for use as admixtures to be used in their formation. For example, the use of sodium nitrite is disclosed in Japanese Patent, Publication No. 33-940, published Feb. 15,1958, application Ser. No. 30-33777, filed December 27, 1955, Kano et al. This patent teaches that sodium nitrite can be added to cement and concrete during mixing to inhibit corrosion of reinforcing iron and steel bars and frames. The aggregate used was sea sand.
U.S. Pat. No. 3,210,207, Dodson et al, teaches the use of mixes of calcium formate with minor amounts of certain nitrite or chromate salts as corrosion inhibitors, to be used as accelerators in cements.
U.S. Pat. No. 3,427,175, Angstadt et al, generically discloses the use of calcium nitrite as an accelerator which partially inhibits corrosion in alite cements. The calcium nitrite may contain minor amounts of sodium nitrite and may be used with calcium chloride and other accelerators.
U.S. Pat. No. 3,801,338, Whitaker, teaches the use of a mixture of calcium formate and sodium nitrite for adding to cement which is to contain metal reinforcement. Improved compressive strength is taught, together with sulfate resistance, and has "a positive corrosion inhibition effect."
The use of sodium nitrite, as taught by certain of the above references, has been found to have detrimental effects of efflorescence and to promote alkali-aggregate reaction within the concrete composition and, therefore, to be a poor corrosion inhibiting agent. The use of calcium nitrite is taught by certain references to be an inhibiting agent when used with any type of cement composition. It has been found that calcium nitrite gives only minimum corrosion resistance when used in the manners described and known by the prior art.
The need for a highly effective corrosion inhibition or a cement composition capable of substantially completely inhibiting corrosion of the metal pieces contained therein over a sustained period of time is highly desired by the building and various other industries which utilize this type of material.